Slim framework is PHP based micro framework. It is can used to write APIs quickly and powerful web applications. For more information on using & installing Slim framework 3.9 please visit official documentation @ https://www.slimframework.com/docs
Let us see how to use Oauth2.0 with slim framework by using bshaffer/oauth2-server-php
more further information, please refer to my github project : https://github.com/chavakula/slim-framework-oauth2
If you have any questions & doubts, please comment below in comments section.